In an effort to reduce greenhouse gas emissions, various research efforts have been devoted to developing technologies to produce fuels and chemical products from renewable resources. Some types of biomass materials that could be valuable for fuel and chemical product production are lignin-containing materials, which can include woody biomass or other biomass containing lignocellulose. Lignocellulose can be used directly as a type of biomass, or a digestion process can be used to separate cellulose from a lignin-containing portion. Various pyrolysis, catalytic pyrolysis, and catalytic fast pyrolysis methods have been proposed for converting lignocellulose and/or lignin-containing materials to compounds that can be more readily converted into desired products. Unfortunately, lignin-containing materials remain a difficult source of biomass to use effectively for production of renewable fuel and chemical products.
U.S. Patent Application Publication No. 2012/0203042 describes methods for pyrolyzing a hydrocarbonaceous feed to produce pyrolysis products. The various methods include using recycle of olefins generated during pyrolysis back to the pyrolysis reaction zone to alter the product composition. The methods also include using variations in pyrolysis temperature and/or catalysts to modify the pyrolysis products.
U.S. Patent Application Publication No. 2011/0275868 describes methods for converting lignin-containing starting materials into a pyrolysis gas, dealkylating the pyrolysis gas, and then separating aromatics of a desired boiling range from the dealkylated pyrolysis gas. The dealkylation process is described as a hydrodealkylation or steam dealkylation in the presence of hydrogen or water. The dealkylation is performed without allowing substantial cooling of the pyrolysis gas relative to the exit temperature of the pyrolysis gas from the pyrolysis process.
U.S. Patent Application Publication No. 2003/0115792 describes methods for converting lignins into a high octane blending component. Lignin is depolymerized using a base catalyzed process, followed by hydroprocessing of the depolymerized lignin to form C7-C10 alkylbenzenes.
U.S. Patent Application Publication No. 2010/0137663 describes methods for hydrogenation and base catalyzed depolymerization for lignin conversion. In an initial step, lignin is hydrogenated to convert aromatics to saturated compounds and to remove some oxygen. This reduces the acidity of the hydrogenated lignin compounds, allowing a lower strength base to be used for base catalyzed depolymerization.
U.S. Patent Application Publication No. 2009/0151253 discloses methods and systems to convert carbonaceous materials (such as biomass) into synthesis gas and other downstream products (such as alcohols). In certain embodiments, pyrolysis is performed in the presence of a catalyst such as heterogeneous catalysts (such as SiO2—Al2O3, Pt/SiO2—Al2O3, WOx/ZrO2, SOx/ZrO2), zeolites (such as HY-zeolite, alpha-zeolite, HZSM-5, ZSM-5, or klinoptilolite), acid catalysts, clay catalysts (e.g., acidified or activated clay catalysts), Al-MCM-41 type mesoporous catalysts, activated alumina, CoMo catalysts, and Ni/Al co-precipitated catalysts. In some embodiments, a cation such as K+, Li+, or Ca2+ can be used to increase the selectivity and yield of char and/or to lower the selectivity and yield of tar during pyrolysis.
U.S. Pat. No. 8,202,332 discloses processes for fractional catalytic pyrolysis of biomass materials. The processes involve the use of a suitable catalyst in a fluidized bed pyrolysis system. Suitable catalysts are described as including H-ZSM-5, an aluminosilicate zeolite catalyst, and super acid catalysts, such as sulfated zirconia super acid catalysts.
U.S. Pat. No. 8,293,952 describes the production of pyrolysis products having a greater stability than pyrolysis products obtained from conventional pyrolysis production processes by using a basic metal oxide catalyst, such as a Group 2, Group 3, or Group 4 metal from the IUPAC Periodic Table of Elements.
U.S. Pat. No. 8,344,197 describes systems and methods for production of xylenes, including para-xylene, by methylation of benzene and toluene in the presence of methanol and a suitable molecular sieve.
It is desirable to improve the quality of bio-oil produced from lignin-containing feedstocks and provide a method for producing aromatics, particularly para-xylene, from lignin.